The present invention relates to the examination of samples able to emit electrons, particularly as a result of a stimulation, caused by an in particular thermal or photon excitation with a view to detecting and locating these electrons.
A first application of this type of examination uses certain sample materials, which, during thermal stimulation, emit an electron flow which can be used for measuring the intensity of a specific excitation previously undergone by the sample. These sample materials are lag time converters of phenomena which it is wished to observe. For example, this first application relates to the examination of converter materials also used more particularly as radiation dosimeters used for the protection of personnel working in areas liable to be irradiated.
Hitherto, these thermostimulated electrons have been detected and located, either with the aid of electron multipliers requiring a high quality vacuum, or by integration in an ionization chamber, or by the use of electron multiplication counters in gases. These different protection processes use precise equipment, which are very difficult, sensitive and therefore costly to manufacture. In addition, they do not make it possible to analyse samples having a large surface, or to simply detect in a separate manner the exoelectrons emitted by several specialized areas of the converter material.
A second application of this type of examination is the location of surface defects. Hitherto, for obtaining information on the structure, homogeneity, composition, etc of surfaces, various methods have been used ranging from optical microscopy with X-ray diffraction, to ultrasonic analysis or scanning electron microscopy. However, these highly technical methods are unsuitable for detecting insipient microcracks, which can be clearly revealed by photon excitation, which causes electron emission.
Thus, the crystalline modifications of materials subject to various stresses are accompanied by dislocations which, on a macroscopic scale, act as electron traps and very locally disturb the Fermi level of the material. Optical stimulation which can be applied in a local and detectable manner releases part of these electrons, thus revealing the presence, at a precise location, of surface defects.